KB 001780 | Structural Design of Windbreak Porous Fabric Structures in RFEM & RWIND

Every day, thousands of structural engineers design structural components using design check formulas that include the critical buckling load. But where do these old formulas come from, that Leonard Euler established over 200 years ago and that form the basis of all three structural steel design concepts?

This paper is focused on the specific aspects of designing membrane structures that have specific requirements, such as form-finding and cutting pattern generation. An integral part of the design of these structures is the process of finding suitable prestressed shapes and generating cutting patterns. The text briefly describes two basic processes in the design of membrane structures. The physical principles are explained and the individual theses illustrated by examples.

Compliance with building codes, such as Eurocode, is essential to ensure the safety, structural integrity, and sustainability of buildings and structures. Computational Fluid Dynamics (CFD) plays a vital role in this process by simulating fluid behavior, optimizing designs, and helping architects and engineers meet Eurocode requirements related to wind load analysis, natural ventilation, fire safety, and energy efficiency. By integrating CFD into the design process, professionals can create safer, more efficient, and compliant buildings that meet the highest standards of construction and design in Europe.

The "Orthotropic | Fabric | Nonlinear Elastic (Surfaces)" material model allows you to define prestressed fabric membranes using the representative microstructure-solid element model – RVE.

By considering the fabric geometry in the microstructure model, the corresponding transversal strain effect can now be considered for all force conditions in the membrane.

The Ponding load type allows you to simulate rain actions on multi-curved surfaces, taking into account the displacements according to the large deformation analysis.

This numerical rainfall process examines the assigned surface geometry and determines which rainfall portions drain away and which rainfall portions accumulate in puddles (water pockets) on the surface. The puddle size then results in a corresponding vertical load for the structural analysis.

For example, you can use this feature in the analysis of approximately horizontal membrane roof geometries subjected to rain loading.

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Compared to the RF-FORM-FINDING add-on module (RFEM 5), the following new features have been added to the Form-Finding add-on for RFEM 6:

• Specification of all form-finding load boundary conditions in one load case
• Storage of form-finding results as initial state for further model analysis
• Automatic assignment of the form-finding initial state via combination wizards to all load situations of a design situation
• Additional form-finding geometry boundary conditions for members (unstressed length, maximum vertical sag, low-point vertical sag)
• Additional form-finding load boundary conditions for members (maximum force in member, minimum force in member, horizontal tension component, tension at i-end, tension at j-end, minimum tension at i-end, minimum tension at j-end)
• Material types "Fabric" and "Foil" in material library
• Parallel form-findings in one model
• Simulation of sequentially building form-finding states in connection with the Construction Stages Analysis (CSA) add-on